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This paper proposes an enhanced transient control strategy for Virtual synchronous generators (VSGs) to address the challenges faced by grid-connected inverters, including DC-side voltage fluctuations, overcurrent, active power dynamic oscillations, and frequency overshoots during transient processes. Firstly, an active closed-loop small-signal model of the optical storage VSG is developed, and the effects of inertia and damping on the system stability are analyzed. Then, the power angular transient characteristics of the VSG are investigated, and the active power deviation factor is introduced to enhance the transient stability. The proposed strategy categorizes the operating phases according to the angular frequency deviation, the active power deviation, and the rate of change of these deviations while preserving the power angle characteristics of the VSG. By adaptively optimizing these parameters, the DC-side voltage fluctuations and overcurrent are effectively suppressed, and the active power and frequency overshoots are reduced. Simulation results verify the effectiveness of the strategy, with active power overshoot reduced by 9.43 %, voltage fluctuation reduced by 8.97 %, and frequency fluctuation stabilized within ±0.13 Hz. These improvements greatly enhance the dynamic performance of the optical storage microgrid and ensure grid stable operation in complex environment.

In high-power hybrid AC/DC distribution systems, multi-port power electronic transformer (PET) encounters challenges such as energy coordination, transient switching, and submodule balancing. In order to address these issues, especially improving transient dynamic performance, this paper proposes a global inertia sharing (GIS) control scheme for a hybrid five-port PET based on modular multilevel converter (MMC), dual active bridge (DAB), and energy storage system (ESS). Firstly, the scheme introduces an inertia sharing (IS) characteristic among internal submodules and external ports based on the capacitor’s properties, analyzing the control quantities and degrees of freedom for controlling IS. Next, according to the mathematical model of the PET, four IS controllers and three balancing controllers are designed for the GIS control scheme to achieve coordinated energy control, optimization of transient performance of the system, balance between submodules, and effectively reduce the number of control parameters and sampling hardware circuits. Additionally, the operation region of the system, power flow modes, and controller parameter selection are analyzed. Validation results in extreme conditions and numerous operating mode switching demonstrate that the proposed GIS control scheme enables seamless switching and submodule balancing under uninterrupted power supply, significantly enhancing system transient dynamic performance and enriching power flow modes.